Supramolecular chemistry focuses on going “beyond” molecular chemistry, which are systems containing more than one molecule. These systems are based on non-covalent interactions such as hydrogen bonds, van der Waals forces, pi-pi interactions and/or electrostatic effects. For instance, a supramolecular polymer is an organic compound which obtains its polymeric properties through combinations of covalent bonds and specific secondary interactions with high physical bond strengths that contribute substantially to the properties of the resulting material. These polymers show unique characteristics due to the presence of additional physical interactions that are based, most typically, on multiple hydrogen bonding interactions, which are named supramolecular interactions.
Supramolecular compounds, such as polymers, are described e.g. in Macromolecules (1995, 28, 782-783) by Lange and Meijer. The method described therein is radical polymerization of e.g. styrene and a maleimide monomer producing H-bonding units containing 3 H-bonds in a row. The resulting polymer was mixed with melamine, leading to supramolecular structure which is quite brittle and has no adequate mechanical properties.
EP 1 310 533 A2 describes an ink composition which contains a dye capable of self-assembling under appropriate conditions, assembling with another analogous dye as well as of forming supramolecular structures. The latter are based on at least three acceptor/donor interactions per interacting unit, whereas at least one of these interactions arises from a heterocyclic unit. Thus, they are difficult to make and therefore expensive.
Sijbesma et al (Science, 278, 1601) discloses supramolecular polymers comprising quadruple hydrogen bonding units that are capable of forming at least four H-bridges with each other leading to physical interactions between different polymer chains. The physical interactions originate from multiple hydrogen bonding interactions (supramolecular interactions) between self-complementary units, which are based on 2-ureido-4-pyrimidones, comprising at least four hydrogen bonds in a row.
WO 98/14504 A1 describes supramolecular polymers containing monomeric units that form H-bridges with one another, whereas the H-bridge-forming monomeric units in pairs forming at least 4 H-bridges with one another. Preferably, the H-bridge-forming monomeric units are self-complementary and constitute an essentially flat structure. The monomeric unit giving rise the H-bridge formation contains most typically a heterocycle and is complex in nature, and therefore difficult and expensive to make.
US 2004/0034190 A1 describes the preparation of supramolecular polymers by copolymerization of monomers containing quadruple hydrogen bonding units with regular monomers. The monomers have a polymerizable group (a), a linking moiety (b) and a structural element (c) which is capable of forming four hydrogen bridges or more. The structural elements (c) contain most typically a heterocycle and are fairly complex in nature. Thus (c), and in particular the monomer itself, is quite difficult to make and therefore expensive.
WO2005/042641 A1 describes the preparation of a supramolecular polymer comprising quadruple hydrogen bonding units within the polymer backbone, wherein at least a monomer comprising a 4H-unit is incorporated in the polymer backbone via at least two-four reactive groups.
In all of these cases, the structural 4-H units giving rise to hydrogen bond formation contains most typically a heterocycle and is complex in nature, and therefore difficult and expensive to make. Owing to their rigidity, there can be difficulties in compatibility, solubility and processability when making or using the supramolecular polymers.
US 2004/0087755 A1 discloses a polyurethane chain polymer with functional groups able to form a supramolecular polymer. They are typically formed from heterocyclic amines reacting with isocyanate end-groups to produce multiple H-bonds per binding units. Due to their nature, the heterocyclic amines are difficult to dissolve or compatibilise with other materials. This limits the number of possible structures that can be produced and their application.
U.S. Pat. No. 6,683,151 B1 describes a compound comprising a reaction product of (A) an isocyanate functional compound of which at least 40 wt. %, relative to the total amount of (A), has a molecular weight of at least about 500, and (B) a nitrogen-containing compound capable of reacting with said isocyanate functional compound (A). This isocyanate functional compound (A) is itself a reaction product between an isocyanate and a compound containing at least one functional group and at least 40% by weight of the latter having a weight average molecular weight of at least about 450. The nitrogen-containing compound (B) is for instance melamine, urea, acetoguanamine, benzoguanamine, cyanamide and/or isocytosine. The reaction product of (A) and (B) has a molecular weight of less than about 20,000 and comprises an effective amount of groups that are able to form reversible intermolecular physical interactions such that a resulting compound shows polymeric mechanical properties at a temperature below a transition temperature. This compound is very complex in nature, expensive and due to the many constraints imparts not a big flexibility in product design.